Various lighting applications require a lighting device to emit a color of a specific hue. In the theater, various colored lights can be used to set the mood of a scene or act. Photographic studios can use different lighting filters to provide an illumination source that complements the subject being photographed. Traffic control lamps use specific colors to indicate the current and near future traffic pattern of intersections. Automobiles have a specific hue of red for brake lights and tail lights. Low-beam and high-beam head lights are required to be within a white color specification. And parking lights have a yellow color specification. Aircraft also have various specifically-colored lights to indicate various things. Even color computer monitors can be calibrated to specific color standards.
The color of a light can drift due to various conditions. The color might change during the lifetime of a particular lamp, for example. Color may change in response to the applied voltage or current to an electrical lamp. Color may change due to wear of a lamp's lens or filter. And color may change when one or more constituent lighting elements of a collective group of elements fails. A color change, due to any reason, can cause a lighting system to fall outside of its color specification.